1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a laser-beam printer, and more particularly to the control of an image forming apparatus in case of connecting a piece of post-processing equipment for performing stapling processing, punching processing or the like to a sheet after image formation thereon.
2. Description of the Related Art
Conventionally, for performing various kinds of processing such as stapling, punching, folding, binding to sheets on which images have been formed, an image forming apparatus capable of connecting a piece of post-processing equipment to the discharge port of the main body of the image forming apparatus has been provided.
For preventing the sheets to be discharged at even intervals from the main body of an image forming apparatus from hindering the processing of a post-processing unit in case of making a piece of post-processing equipment perform post-processing, it is necessary to hold a large interval between the sheets to be discharged, or to buffer (retain) the sheets to be discharged at the former stage of the post-processing unit. Among inexpensive apparatus having low level productivity, there is one widening the intervals of the sheets to be discharged, but generally a lot of pieces of post-processing equipment has the buffer function for heightening the level of productivity.
Moreover, an image forming apparatus performing the control of preventing the lowering of the level of productivity at the time of a two-sided copying mode previously has been proposed (for example, U.S. Pat. No. 5,778,300).
However, the above-mentioned conventional image forming apparatus has a problem of being large in size and increasing in cost of the main body of the image forming apparatus and a piece of post-processing equipment owing to the space for a buffer unit and a driving mechanism in the case where the buffer function is disposed in the inside of the main body of the image forming apparatus or in the inside of the post-processing equipment.